747-400 range question

[slim75]

ladies and gentlemen,

can someone please explain to me how carriers are able to operate the 744 (non extended range) on legs as long as VHHH-KORD which is over 7700nm?? i'm sure the high latutudes of the polar route help but isn't this range beyond the normal range of the aircraft?? are carriers weight-limiting them inorder to carry more fuel? any insight would be greatly appreciated.

kind regards,

[CR2]

Limited payload.

ELLX-PHNL 747-400F. Special charter flight (the 2 yachts for the Waterworld movie, Kevin Costner etc which were built in France) Aircraft was volumetrically full with about 25T payload. 7500NAM, reclearance (redispatch if you prefer), reserves were an interesting calculation. Max tanks fuel. Made a profit too.

Edit to say: I think it was BA that did EGLL-YSSY non-stop on a 400 pax to set a record. Unsure if they made any profit out of it.

[arem]

Think it was QF that did the SYD non-stop.

[Brian Abraham]

You can read an article written by the record setting QF Captain here http://www.pprune.org/dg-p-reporting-points/76314-chrissy-present-qantas.html

[galaxy flyer]

CR2

I don't think QF intended to make a profit on that flight, but they are KDFW-YBBN!

Anyway, how did you redispatch facing 2200nm of water? Was your redispatch point PANC?

GF

[misd-agin]

DFW - Brisbane shows one stop in LAX on the Qantas website.

[misd-agin]

slim75 - payload restriction.

Boeing performance charts -

http://www.boeing.com/commercial/airports/acaps/7474sec3.pdf

Range goes over 8000 n.m. Chart doesn't show even lighter payload weights, which would allow even longer flights.

[CR2]

QF it is then. Thanks, I wasn't quite sure.

GF

That HNL flight was IIRC Nov 93, very shortly after CLX got its first 400Fs. I also remember it was -15C @ ELLX, so would assume we got a few more gallons in the tanks than usual. (I loaded that damned aircraft, nose and side doors open, howling wind to make life perfect. At 430am).

As Loadmaster I couldn't possibly discuss redispatch points. Other to say that they were long and involved :} (As a matter of fact, I simply don't remember the WHERE).

I guess its correct to say that some aviation authorites have different criteria than others.

[slim75]

thank you for the replies... and copy of the weight limitation and performance charts misd-agin... Thanks!! a follow on question if i may regarding the 747 400BCF.. a thread was started a few years ago regarding the external differences of the BCF from other 747 variants. but what about internal differences.? specifically, did boeing remove the HST system (horizontal stab fuel tanks) from the BCF or did the company leave them in? and does the 747 400F and 747 800F have HSTs?

kind regards,

[RandomPerson8008]

The BCF's, at least at my company, have had their horizontal stabilizer fuel tanks removed. The purpose built -400 freighters do not have horizontal stabilizer tanks. The -8 Freighter does not have horizontal stabilizer tanks either. The -8 Intercontinental appears to still have the stab tanks; like the -400, its listed fuel quantity is roughly 10,000 kilograms greater than the freighter's.

Granted I'm still an ultra neophyte to the world of 747's and freight, but, it's my understanding that zero fuel weight is the limiting number for the freighters on most missions. Filled to maximum zero fuel weight, the 747-400F can only take on roughly 100,000 kilograms of fuel, over 60,000 kilos shy of capacity even without horizontal stabilizer tanks. The number of missions in which the stabilizer fuel might be used apparently did not justify the cost of the equipment, not to mention the added maintenance. In addition the freighter is already considered "tail heavy" in regard to center of gravity....whether or not that factored into the design process I cannot say.

[spannersatKL]

CR2 Sorry I assume you mean a few Kgs more and not a few 'gallons' more fuel!! The same volume more weight!

[NSEU]

Edited due error (memory fade)

[Capt Fathom]

The Qantas flight from London to Sydney was an -ER version

No it wasn't. It was the delivery of the first 747-400 to Qantas. VH-OJA

misd-agin Reference the Dallas-Australia flights.

They will operate Sydney-Dallas-Brisbane-Sydney.

[slim75]

RandomPerson8008- thanks a bunch for the clarification and it makes alot of sense. i also understand that the ZFW is maximized with the freighter models which limit their range due to the priority of the carrier being the freight.
lastly, seeing as you fly the platform, have you noticed a change in epr when you set it on takeoff roll?? does it decrease/increase at all??

kind regards,

[RandomPerson8008]

RandomPerson8008- thanks a bunch for the clarification and it makes alot of sense. i also understand that the ZFW is maximized with the freighter models which limit their range due to the priority of the carrier being the freight.
lastly, seeing as you fly the platform, have you noticed a change in epr when you set it on takeoff roll?? does it decrease/increase at all??

I have only flown the simulator so far...in any case 95% of my company's aircraft have GE CF6-80C2 series engines, as do the simulators. The GE uses N1 as the primary engine indication and does not provide EPR indications. During preflight, the FMC calculates a target N1 value for the engines based on atmospheric conditions and thrust setting selections. The engines spool up to maintain this target N1 after the "TOGA" buttons are pressed at the beginning of the takeoff roll. The N1 % does not change until flaps reach 5 degrees or 1500 ft depending on the departure profile. The thrust change is normally a reduction to climb thrust, however takeoff thrust is maintained until Vref30+98 knots is reached in the event of an engine failure (in which case continuous thrust is subsequently commanded).

Whether EPR indications on Pratt and Whitney and Rolls Royce engines remain constant during the takeoff roll I cannot say for certain because I have no experience with them. Logically the EPR should stay relatively constant once stabilized for takeoff, much like N1, and my differences manuals make scant mention of the subject.

[main_dog]

Assuming EECs are in normal mode and autothrottle is armed for departure, upon pressing a TOGA switch the autothrottle will set the FMC-selected reference thrust (ie the target takeoff EPR for RRs and PWs). This will be done by 65 kts, at which point the autothrottle servos will disconnect ("HOLD" mode) and provided neither pilot touches the throttles, the EECs will ensure that the EPR that was set remains constant. From our FCOM 1: When the engine is stabilized, EEC keeps thrust constant independent of outside air temperature and pressure.

At 400' the autothrottle will re-engage ("THR REF" mode) and when the reference EPR changes (normally at thrust reduction altitude), the thrust levers will be moved accordingly. So in answer to your question, from setting takeoff thrust until at least 400' AAL when the A/T re-engages, the EPRs shouldn't change.

MD

PS Speaking of higher ZFWs on the freighters, on our 747-400ERFs normal MAXZFW is 277,144 kgs and can even go as high as 288,031 kgs albeit with a lowering of the MTOW... :eek:

[slim75]

MD, thanks for your insights. any chance you can clarify for me what EEC stands for??

Regards,

[RandomPerson8008]

EEC stands for Electronic Engine Control. It is similair to a FADEC, however less advanced in my opinion. The EEC provides overspeed protection, adjusts fuel flow to compensate for various atmospheric conditions, and provides thrust limiting. On the 747 each engine has one EEC which is powered by a dedicated electrical generator through the accessory gearbox.

[Taildragger67]

Just to clarify:

- the record flight from EGLL to YSSY was the delivery flight of Qantas's first 747-438, in 1989. It was not a 747-438ER (the first of which was delivered in 2002), rather a 'normal' -400 and had delivered across from Seattle before being filled with special fuel for the record flight;

- Qantas has not yet started operating its own equipment to KDFW, hence current schedules KDFW-YBBN would show a stop (transfer) in KLAX;

- Qantas will shortly be operating its own equipment (747-438ER) from Australia to DFW and back, running YSSY-KDFW-YBBN-YSSY, the BNE stop being required on the way back as the aircraft can't reliably fly KDFW-YSSY all year with revenue payload.

Anorak mode OFF...

[main_dog]

any chance you can clarify for me what EEC stands for??


What Random Person said. I believe the 744's EECs don't qualify as FADECs because they don't control variable bleed valves or variable stator vanes (VIGVs for the RR), but I defer to any engineer on these finer points of engine control... me simple pilot, move thrust levers forward = yippee

:}

MD

[slim75]

MD and Random Person thanks for the clarification. if i may ask you further, over the life of an RB-211-524, PW 4056 and GE CF6, does the thrust produced by the engines decrease over time? would a constant N1 or EPR setting over time equate to a reduction in total thrust of that engine??

[RandomPerson8008]

Yes....most of the airplanes at my company came with CF6-80C2B5F engines installed, rated for 62,100 lbs of Boeing equivalent thrust. Over time, they become de-rated to CF6-80C2B1F engines which are rated for 56,500 lbs. The decisions regarding when and why to accomplish these de-rates are usually made by the engine owner/lessor, to the best of my knowledge.

Maximum N1 & N2, 117.5% and 112.5% respecitvely, remain the same for both B1F and B5F variants. Therefore, one might conclude that for a given N1 value, less thrust is being produced by the derated engine.

So...does the thrust produced by engines at a given N1/EPR degrade over time? Yes, I would say so. Does this happen appreciably even prior to the de-rates being established for a given engine? I do not know for certain, but logically one would say yes, a new engine probably performs closer to rated specifications than an old and worn out one. Wear and tear on the engine's blades likely leads to less efficient compression and therefore less thrust being produced at a given RPM. An engine mechanic would be a much better person to ask this question to, since they are undoubtedly the ones responsible for monitoring engine performance and making sure the engine is overhauled or replaced once it degrades beyond limits.

[main_dog]

does the thrust produced by the engines decrease over time? would a constant N1 or EPR setting over time equate to a reduction in total thrust of that engine??

Again one for the techs, not for pilots... but I'll give it a shot.

EPR is a fairly direct measure of thrust, thus assuming the pressure/temperature probes/gauges are working correctly, 1.72 EPR on a new engine should be equal thrust to 1.72 on an old one. What will change is how hard the engine has to work to produce that thrust: the older engine will probably show a higher EGT, fuel flow and indeed N1 to produce the same thrust.

N1 is a measure of engine rotation, so I would imagine an older engine turning at 111.4% N1 will not be producing as much thrust as a new one showing 111.4%... stand to be corrected though.

MD

PS When's a techie when you need one? :}

[misd-agin]

757 RR engines used to be 43,100. Now they're rated at 42,700.

Don't know if the change was due to age or some other, unknown, reason.

[misd-agin]

Taildragger67 and Capt Fathom - Thanks, I was looking at days that the non-stop wasn't flown.

16+00 DFW - BNE. 747-400 QF8 non-stop.

[slim75]

Thank you for your insights into my inquiries... your explanations make sense to me. And your're right, a mechanic would be more appropriate to ask however i think that some commercial companies ask this type of question in a pilot interview. just trying to prepare myself.

Regards,

[Check Airman]

Over time, they become de-rated to CF6-80C2B1F engines which are rated for 56,500 lbs.

How does the engine designation change after leaving the factory. I appreciate that an older engine may not pack as much of a punch as a new engine, but how does one change the model number of an engine?

[RandomPerson8008]

The B5F/B1F switch is apparently just an EEC "software change". That's why it can be done after the engines leave the factory. I've seen similar model designation and thrust changes take place on other FADEC equipped engines.

[Check Airman]

thanks for that info

[SMOC]

EPR does drop during takeoff due to Ram effect which starts at around 80kts.

[Nepotisim]

Random person, before you start scaring pilots out there.:eek:

Engines do not become derated over time. They always produce rated thrust if requested.

As the engines get older the EGT margin decreases. ie The older the engines get the closer they get to max EGT on a max rated thrust takeoff. When this happens you can remove them from a CF6-80C2B5F rated aircraft and install them on a CF6-80C2B1F rated aircraft (Rating change via plug change/pin programming). You then get longer out of them before you have to overhaul because at a lower rating it is like doing a derated takeoff and the EGT margin returns.For a while at least anyway.:ok:

So in summary. If the book says the engine is good for 63500 lbs. Then a new engine and a 30000hr engine will produce said thrust. The older one will be hotter.

I believe the 744's EECs don't qualify as FADECs because they don't control variable bleed valves or variable stator vanes (VIGVs for the RR), but I defer to any engineer on these finer points of engine control

744's do have EEC's. EEC is a generic term, possibly even a Boeing term. Each manufacturer has their own term.
Rolls Royce call them FAFC. Full authority fuel control.
Pratt & Whitney call them FADEC. Full authority digital engine control.
GE call them ECU. Electronic control unit.

You are correct that on a 744 RR that the FAFC doesn't control the VIGV's or bleed valves, but thats only because RR choose to do it that way. (They are pneumatically controlled)
GE do however control both of those items by the ECU via the HMU (Hydromechanical unit or carby);)

[RandomPerson8008]

Thanks for the correction, Nepotism.